The detection of the Acquisition Indicator Channel (AICH) according to 3rd generation partnership project (3GPP) specifications is part of the random access procedure. The procedure can be described as follows. In order for a terminal or a user equipment (UE) to send a Random Access Channel (RACH) message, it first needs to decode the Broadcast Channel (BCH) to find out what are the available RACH sub-channels, scrambling codes, and signatures. The UE selects randomly one of the RACH sub-channels from the group its access class allows it to use. This implies a restriction on when a RACH preamble can be sent. Then the signature is selected randomly. There are sixteen signatures available, which means that sixteen UE can send at the same time. The downlink power level is then measured and the uplink power level is set with proper margin due to open loop inaccuracy. A 1 ms RACH preamble is sent with the selected signature. The UE then listens for a confirmation from the base-station. The confirmation is sent through the AICH. In case no AICH is detected, the UE increases the preamble transmission power by a step given by the base station. The preamble is then retransmitted in the next available access slot. When finally an AICH transmission from the base-station is detected in the UE, the UE transmits the 10 ms or 20 ms message part of the RACH transmission.
A RAKE receiver is typically used in digital wireless communication systems to improve the performance of a CDMA (Code-Division Multiple Access) receiver by utilizing signal energy carried by many multipath components. In a RAKE receiver this is achieved by letting each multipath component be assigned a despreader whose reference copy of the spreading code is delayed equally to the path delay of the corresponding multipath component. The outputs of the de-spreaders (fingers) are then coherently combined to produce a symbol estimate. The RAKE receiver uses knowledge of the multipath delays and the values of the channel impulse response for all paths.
One prior art method of and device for signal detection simply uses a summation of the sent AICH symbols, which is less robust and does not provide reliable detection, especially when a detector moves at a relatively high speed due to fading.
EP 1170880 discloses a radio base station device and radio communication method that enables adaptive array antenna (AAA) reception by a RACH and AAA transmission by an AICH and reduced interference with other base stations.
However, this device and method does not provide reliable detection when moving at relatively high speed, since the problem of avoiding the effects of fading that makes the signal strength vary is not addressed. Further weights are not derived. Instead an already known signal section (preamble section) of the RACH is used.